Blade-type electric fuses



Oct. 6, 1964 F. J. KOZACKA BLADE-TYPE ELECTRIC FUSES 2 Sheets-Sheet 1Filed March 21, 1961 IIIIJ Oct. 6, 1964 Filed March 21,

F. J. KOZACKA BLADE-TYPE ELECTRIC FUSES 2 Sheets-Sheet 2 United StatesPatent 3,152,233 BLADE-TYPE ELECTRIC FUSES Frederick J. Kozacka, SouthHampton, N.H., assrgnor to The Chase-Shawmut Company, Newburyport, Mass.

Filed Mar. 21, 1961, Ser. No. 106,994

Claims. (Cl. 200-120) This invention is concerned with electric fusesfor protecting electric circuits against excessive currents, and it ismore particularly concerned with current-limiting fuses.

It is a widely accepted practice to close the fuse tubes or casings offuses intended to have a relatively high current carrying capacity and arelatively high interrupting capacity and to be current limiting bycopper plugs the axially outer surfaces of which support a pair ofaligned blade contacts.

Structures of this kind are relatively expensive. It is, therefore, oneobject of this invention tOl provide electric fuses of the blade contacttype having a relatively high current carrying capacity and a relativelyhigh interrupting capacity and which are current-limiting, which fusesare easier to manufacture and involve smaller manufacturing cost thanthe above referred-to type of fuses provided with terminals in the formof copper plugs.

Another object of this invention is to provide electric fuses having aparticular kind of fuse links which will hereinafter be referred to aslattice links, in which fuses a pair of lattice links is associated witha pair of blade contacts for connecting that pair of lattice links intoan electric circuit.

Another object of the invention is to provide electric fuses Whichhaveterminal elements in the form of a pair of blade contacts projectingthrough a pair of caps closing both ends of the fuse tube or casing,which fuses have a very small voltage drop across said pair of bladecontacts when performing their normal current carrying duty, whereinheat generation is thus minimized and which run cool as a result ofminimized heat generation.

This application is a continuation-in-part of my copending patentapplication Ser. No. 764,293, filed September 30, 1958, for Time-LagFuses, now United States Patent 2,988,620, issued June 13, 1961.

It is a further object of this invention to provide improved versions ofthe electric fuse disclosed and claimed in my above referred-tocopending patent application.

My above referred-to patent application is concerned with fuses of thetime-lag type and it is, therefore, another object of this invention toprovide improved electric fuses making it possible to achieve time-lagin the same fashion as disclosed and claimed in the above patent.

Another object of the invention is to provide currentlimiting fuseswherein the number of serially related points of reduced cross-sectionor necks is minimized without impairment of the current-limiting abilityof the fuses.

Still another object of the invention is to provide current-limitingfuses wherein the current prevailing at the points of reducedcross-section or neck is relatively small.

Other objects of the invention and advantages thereof will, in part, beobvious and in part appear hereinafter.

For a more complete understanding of the invention reference may be hadto the following description thereof taken inconnection with theaccompanying drawings, in which:

FIG. 1 is a longitudinal section of an electric fuse embodying thisinvention taken along 11 of FIG 2;

FIG. 2 is a longitudinal section of the fuse shown in FIG. 1 taken along2-2 of FIG. 1;

FIG. 3 is a longitudinal section of another electric fuse embodying thisinvention taken along 3-3 of FIG. 4; and

"ice

FIG. 4 is a longitudinal section of the fuse shown in FIG. 3 taken along4-4 of FIG. 3.

Referring now to the drawing, and more particularly to FIGS. 1 and 2thereof, numeral 1a has been applied to indicate a tubular casing ofinsulating material, e.g. of a synthetic resin-glass-cloth laminate. Theaxially outer ends of easing or fuse tube 1a are closed by a pair ofmetal caps 2a crimped on the axially inner ends thereof into casing 1ato establish a strong mechanical connection or tie between casing 1a andcaps 2a. Aligned blade contacts 4a made of flat copper stock projectfrom the outside of casing 1a transversely through the end surfaces ofcaps 2a into the inside of casing 1a. To this end each cap 2a isprovided with a rectangular cutout 2a having substantially the samegeometrical configuration as the cross-section of blade contacts 2a.Circular washers 3a having rectangular cut-outs similar to the cut-outsin caps 2a are interposed between caps 2a and the axially outer ends ofcasing 1a. Pins or pinshaped springs 4a project transversely acrosscasing 1a and blade contacts 40. Pins 4a are intended to secure bladecontacts 4a to casing 1a and to maintain the same axially alignedtherein. The aforementioned pin structure has been only diagrammaticallyindicated in FIGS. 1 and 2. Preferably this structure is designed alongthe lines fully disclosed in my United States Patent 2,939,935 issuedJune 7, 1960, for Fuse Structures, and reference may be had to thatpatent for a full disclosure of the preferred pin structure intended forthe embodiment of the invention shown in FIGS. 1 and 2. The axiallyinner ends of blade contacts 4a are conductively interconnected by apair of ribbon-type fuse links 5a of sheet metal and easing 1a is filledwith a pulverulent arcquenching filler 6a, e.g. quartz sand, in whichfuse links 5a are submersed. Fuse links or fusible elements 5a have thesame width as blade contacts 4a, the width W of which has been indicatedat the left of FIG. 1. The width W is slightly less than the innerdiameter of casing 1a. It is not absolutely necessary that the width offuse links 5a be exactly equal to that of blade contacts 4a, but it isimportant that the width W of fuse links 5a be approximately, orsubstantially, equal to that of the blade contacts 41:, and that thelatter is as large as possible. Each of links 5a defines a latticeconsisting of parallel connected necks and of serially connected necks.A neck of a fuse link is a point thereof where the current density islarger than the current density prevailing at the points of the fuselink where its cross-sectional area is largest and its current-densityaccordingly smallest. Each fuse link 5a is provided with five transverselines U, R, S, T, V defined by circular perforations forming fivetransverse lines of necks. The axially outer lines of perforations U, Vare superimposed upon blade contacts 4a and the axially inner lines ofperforations R, S, T define necks generating a circuit-interrupting arcvoltage when the fuse blows. Reference characters x x x x have beenapplied to indicate the necks formed by transverse line of perforationsR. Reference character x x x x have been applied to the center line ofnecks formed by the transverse center line S of perforations, andreference characters x x x x have been applied to indicate the necksformed by the line of perforations T. The aggregate width 2W of links5;: is relatively larger, and the thickness of links 5a is relativelysmaller, than the width and thickness of conventional fuses having acomparable current rating. This tends to greatly decrease the currentdensity at each neck, and the magnitude of the arc current which flowsacross each gap formed upon blowing of the fuse at the point of eachneck.

It is a generally accepted design principle to increase the number ofseries necks forming series breaks in proportion to the voltage of thecircuit in which a particular fuse is intended to be used. Where a fuseis expected to exhibit a substantial current-limiting action the numberof series necks forming series breaks is particularly high since itrequires high initial arc voltages to rapidly force a major faultcurrent down to zero. It is a generally accepted practice in the designof low-voltage currentlimiting fusesi.e. current-limiting fuses having avoltage rating of 600 volts or less-to provide the fuse links thereofwith a relatively large number of series necks forming series breakswhen the fuses blow.

The links or fusible elements of current-limiting fuses having a voltagerating of 600 volts, particularly if such fuses are intended forrelatively high current ratings, have generally as much as five seriallyconnected necks forming five series breaks when the fuses blow on majorfault currents. FIGS. 1 and 2 (and also FIGS. 3 and 4) show acurrent-limiting fuse structure having a voltage rating of 600 volts buthaving only three effective transverse lines R, S, T of necks ratherthan five such lines. In the structure of FIGS. 1 and 2 the effectivenumber of transverse lines of perforations is three rather than fivesince the perforations of the axially outer transverse lines U, V areshunted by knife blade contacts 4:: and, therefore, ineffective. Thisdrastic reduction in the number of transverse lines of necks or circularperforations greatly reduces the voltage drop across the blade contacts4a while the fuse is performing its normal current carrying duty, and italso reduces greatly the watt losses due to the voltage drop and thustends to be conducive to a cool running fuse structure.

As shown in FIG. 1 each link 5a is provided with a system of circularperforations having centers arranged in a lattice pattern. Theseperforations define a system of necks which are likewise arranged in alattice pattern. Thelattice pattern of circular perforations includes afirst family of parallel lines R, S, T extending transversely acrosseach link 5a and a second family of parallel lines at right angles tosaid first family and extending in a direction longitudinally of casingin. The second family of lines includes seven parallel spaced lines.There are six parallel lines of series necks between each of said secondfamily of lines of perforations, namely lines of necks x x x x x x x x xx x x" It will be apparent that the number of the above referredtolongitudinal lines exceeds by far the number of transverse lines R, S,T. This is but one way of saying that the number of necks arranged, orconnected, in parallel in each of the three transverse lines R, S, Texceeds by far the number of serially connected lines of necks, thefirst mentioned number being six and the last mentioned number beingthree. The number of the serially connected lines R, S, T of necksdetermines the magnitude of the arc voltage immediately upon blowing ofthe fuse under major fault conditions. That arc voltage increases inproportion to the number of serially connected lines of necks.

Upon having reached a peak value the arc voltage decays at each point ofbreak more or less rapidly, the rate of decay depending inter alia uponthe heat generated at the particular point of break and the latterdepending upon the density of the arc current at each point of break.

It will now be apparent why the lattice structure shown in FIGS. 1 and 2makes it possible to achieve in a 600 volt circuit substantially thesame current-limiting action which, in comparable prior artcurrent-limiting fuses, called for five series breaks, or five seriallyconnected lines of breaks. The reduction in a number of series necks, orthe number of serially connected lines of necks, greatly reduces theinitial arc voltage, but the increase of the number of necks in eachtransverse line of necks greatly reduces the current at each neck orpoint of break, the heat generated at each point of break andconsequently the rate of the decay of the arc voltage at each point ofbreak. This is conducive to a more or less steady or stable arc voltage,or flat top are voltage, which is the ideal type of arc voltage. Thisideal can never be fully attained. Fuse links of the type shown in FIGS.1 and 2 are, however, conducive to generating a fair approximation tothe ideal arc voltage.

The reduction of the number of series necks, or serially connected linesof necks, and the concomitant increase of the number of parallelconnected necks per line are not only conducive to arc voltages havingrelatively small initial peaks and relatively small rates of subsequentdecay, but are also conducive to relatively small voltage drops acrossthe fuse while the latter is performing its normal current carrying dutybefore occurrence of a major fault current.

The cross-sectional area Q max. of a fuse link of perforated sheet stockat any point thereof where the fuse link is not perforated is largelydetermined by the current carrying capacity which is required of thefuse of which the fuse link forms a part. The cross-sectional area Qmin. of a fuse link of perforated sheet stock at any point where itscross-section is reduced to a minimum is determined by the requiredfusing i -t value of the fuse of which the fuse link forms a part. Todecrease in any given design the number of transverse lines ofperforations and to increase the number of perforations per line withoutchanging the voltage rating and current rating and the current-limitingability of the particular fuse structure therefore means to greatlyreduce the thickness of the sheet metal of which the fuse link is made,varying its Q max. Within limits, and maintaining its Q min. unchanged.

In order to minimize the current per neck two links 5a are connected inparallel, and each of the two links 5a is made as wide as possible, i.e.approximately as wide as the pair of wide blade contacts 4a projectingthrough caps 2a. If a fuse intended for a given current carryingcapacity is designed in this fashion the ribbon links thereof have atendency to become thinner than those in conventional fuses having thesame current carrying capacity or current rating. This, in turn, makesthe fuse links 5a considerably more fragile. To prevent damage to thevery thin and fragile fuse links 5a each link 5a is supported by aninsulating plate 7a preferably made of a synthetic resin-glass-clothlaminate, e.g. a melamine-glass-cloth laminate. Plates 7a are arrangedon juxtaposed sides of links 5a. Links 5a may be affixed to insulatingplates 7:: by means of staples 9a projecting transversely through thelinks 5a and the insulating plates 7a. In addition to supporting links5a, plates 7a form effective barriers against the flow of products ofarcing into the space between links 5a. The transverse lines ofperforations, U, V superimposed upon blade contacts 4a facilitatesoldering of the axially outer ends of links 5a to the axially innerends of blade contacts 4a. These two lines of perforations do notperform any function upon assembly of the fuse when the latter performsits current carrying and interrupting duty and may, therefore, beomitted, if desired. Each link 5a has axially outer bent portions 5aenclosing an angle of degrees with the general plane of blade contacts4a. Bends 5a are situated between the axially outer ends of metalribbons 5a and the axially outer edges of insulating plates 7a. Bentportions 5a impart increased flexibility, or give, tothe link structure,which properties are required because of the fragility of the latter. It

will be apparent from FIGS. 1 and 2 that forces of compression, tensionor torsion resulting from misalignment of blade contacts 4a are nottransmitted to the fragile neck portions of links 5a.

Each link 5a is made of a metal having a relatively high conductivityand a relatively high fusing temperature, preferably silver or copper.The conductivity of silver is 62.6 and the fusing point of silver is960.5 deg. C. The conductivity of copper is 58.8 and the fusing point ofcopper is 1083 deg. C. The conductivity of 'point metal such as silverand copper.

tin is 9.4 and the fusing point of tin is 231.8 deg. C. Tin is a typicallow fusing point metal. Zinc has a conductivity of 16.95 and a fusingpoint of 419.4 deg. C., i.e. its conductivity is less than one third ofthat of a high conductivity metal such as silver and copper, and itsfusing point is less than one half of that of a high fusing Highconductivity, high fusing point metals such as silver and copper havesmall fusing i -t values and are, therefore, necessary and desirable formaking fuse links for current limiting fuses. Each link 5a is providedwith an overlay 8a of a metal having a relatively low fusing point, e.g.tin, capable, upon fusion thereof, to destroy the base metal by ametallurgical reaction and thus to form a break. Such overlays are wellknown in the fuse art as a means for achieving time-lag and formingbreaks on the occurrence of relatively small protracted overloads, asdistinguished from major fault currents. Overlays 8a are arranged onremote sides of links 5a. It will be apparent from FIG. 1 that overlays8a are coextensive with the entire Width of ribbons 5a and substantiallyparallel to the transverse family of lines defining a lattice pattern ofnecks, and the lattice pattern of circular perforations, respectively.Overlay 8a has a family of longitudinal projections extending to, butnot beyond, the transverse line S along which necks x x x x are aligned.As a result of this geometry, on occurrence of major fault currents allnecks aligned in line S will fuse substantially simultaneously with allnecks aligned in lines R and T, whereas on occurrence of small butprotracted and inadmissible overloads but the necks aligned intransverse line S will be severed by the action of overlay 8a. Thusnecks x x x x are dual function necks, forming breaks on occurrence ofmajor fault currents as well as on occurrence of relatively smalloverloads of inadmissible duration. This dual function feature of thenecks aligned along transverse line S makes it possible to rapidlyinterrupt circuits having a circuit voltage of, and as high as, 600volts by resorting to but three serialy connected lines R, S, T ofnecks.

The structure shown in FIGS. 3 and 4 is similar to that shown in FIGS. 1and 2 and operates in substantially the same fashion as the latter.Referring now to FIGS. 3 and 4, tubular casing 1b is closed on both endsthereof by caps 2b having rectangular cutouts 2b through which bladecontacts 4b project from the outside of the casing into the insidethereof. Casing 1b is filled with a pulverulent arc-quenching filler 6b,e.g. quartz sand, and washers 3b preclude the same from leaking out ofcasing lb. Pin springs 4b project through casing 1b and blade contacts4b, integrating these two parts into a structural unit. A pair of ribbontype fuse links 5b sandwiches at the axially outer ends thereof theaxially inner ends of blade contact 4b. Each fuse link is provided witha lattice of circular perforations defining a lattice of necks, bothlattices being the same as those shown in FIGS. 1 and 2 and more fullydescribed in connection therewith. The lattice area of both fuse links5b is backed up by insulating plates 7b which are coextensive with saidarea. Staples 9b projecting through links 5b and insulating plates 9bmaintain the latter in their proper position. The center line S ofperforations and necks is associated with an overlay 8b of tin or otherlow fusing point metal for severing the base metal by a metallurgicalreaction on occurrence of relatively small overloads of inadmissibleduration. Each fuse link 5b is provided with a substantiallysemicircular bend 5b situated between the axially inner edges of bladecontacts 4b and the axially outer edges of insulating plates 7b. Thesebends impart a certain flexibility to the structure and help to protectthe perforated portion of the links 5b against stresses and strainswhich may result from external forces acting on blade contacts 4b.

For reasons of clarity the section plane 1-1 of FIG. 2 and the sectionplane 33 of FIG. 4 are shown in spaced relation from the upper surfaceof blade contacts 4a and 41;, respectively, and from the upper surfaceof fuse links 5a and 5b, respectively. Actually both these sectionplanes are supposed to coincide with the upper surfaces of the bladecontacts and of the upper surfaces of the fuse links. Each circularperforation in fuse links 5a and 511 respectively accommodates a thinlayer of pulverulent arc quenching filler 6a and 6b respectively clearlyshown in FIGS. 1 and 3, and therefore the portions of the blade contactsand the portions of the insulating plates below that thin layer are notexposed to view.

When the fuse structure shown in FIGS. 1 and 2 is carrying current atemperature gradient is established in the direction longitudinally oflinks So as well as in transverse direction. The highest spottemperatures occur in necks x and x When the overlay 8a covering necks xand x melts, these two necks are severed by metallurgical reaction andthe current continues to flow through the remaining necks x x x x inline S. Soon the overlay on necks x x melts and all the current is thenconcentrated in necks x x After these two necks have been severed by theaforementioned metallurgical reaction the current paths through links 5aare interrupted.

Interruption on occurrence of major fault currents such as short-circuitcurrents is effected in a similar sequence of partial link-severingprocesses. The temperature is highest in necks x x x x x x immediatelyadjacent the center perforations and decreases toward the twoimmediately adjacent radially outer perforations. Melting begins at thepoints Where the temperature is highest. Small droplets of liquefiedlink metal are formed at these points. These droplets have a tendency toflow in transverse direction toward cooler points of the link, thistendency being due to the surface tension of the liquefied metal. Thereis thus a tendency of formation of transverse gaps beginning with atransverse en largernent of the perforations intersected by plane 22, ora transverse restriction of necks x x x x x x When these necks arecompletely severed by fusion, fusion and severance of necks x x x x x xbegins. When fusion and severance of these necks has been completed,necks x x x x x x are caused to fuse and to be severed. Arcing beginswhen the last mentioned necks are fused and severed. It has been foundthat arcing is not limited to the points where fusion occurs last. Whenlinks 5a are completely severed in transverse direction along lines R,S, T arcing occurs along the entire width of the transverse gaps thusformed. Back burning occurs likewise along the entire width of thesegaps, and thus the heat generated during the arcing period is evenlydistributed, minimizing the decay of the arc voltage after kindling ofseries are at lines R, S, T.

The operation of the structure of FIGS. 3 and 4 is, in substance, thesame as that of FIGS. 1 and 2.

Where there is no need for overload protection involving time lag, butmerely one for protection against major fault currents or short-circuitcurrents, overlays 8a (FIGS. 1 and 2) and 8b (FIGS. 3 and 4) may beomitted.

The fuse structures shown in FIGS. 1-4 are primarily intended for A.C.circuits having a circuit voltage up to and of 600 volts. They are notadapted for interrupting high D.C. currents at voltages as high as 600volts, but may be used in DC. circuits if appropriately derated. Theback-burning of the ribbon links of these fuse structures is verylimited. Hence the total length of ribbons 5a and 512, respectively, canbe less than 3 inches.

For reasons of greater clarity a different direction of the hatchinglines has been adopted in FIGS. 2 and 4 to indicate the arc-quenchingfiller in the space between the ribbon links 5a, 5b and outside of thesame. It will be understood, however, that there is actually an integralbody pulverulent arc-quenching filler throughout the entire casing.

It will be apparent from the foregoing that this invention provides anovel type of high interrupting capacity or current-limiting fuses whichis strictly opposed to the current trend in the design of highinterrupting capacity or current-limiting fuses inasmuch as the currenttrend is toward increasing the number of serially connected necks forany given circuit voltage, whereas this invention is predicated upondecreasing the number of serially connected necks for any given circuitvoltage. This is made possible by reducing the thickness of the ribbonlinks and concomitantly increasing both the width thereof and the numberof perforations per transverse line of perforation. It thus becomespossible to successfully interrupt circuits having a circuit voltage of600 volts with ribbon fuse links having but three transverse lines ofperforations, or one line of transverse perforations per 200 volts, orfor each 200 volts, circuit voltage.

It Will be further understood that I have illustrated and describedherein preferred embodiments only of my invention and that variousalterations may be made in the details thereof without departing fromthe spirit and scope of my invention as defined in the appended claims.

I claim:

1. An electric high interrupting capacity fuse comprising incombination:

(a) a substantially tubular casing of insulating material having apredetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined Widthbut slightly less than said diameter each projecting from the outside ofsaid cas ing through the end surface of one of said pair of terminalcaps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having arelatively high conductivity and a relatively high fusing pointapproximately equal in width to said predetermined width conductivelyinterconnecting the axially inner ends of said pair of blade contacts,each of said pair of ribbons including a lattice pattern area of necksconnected in parallel and of serially connected necks, said latticepattern area being formed by substantially transverse lines ofperforations, each of said lines of perforations including apredetermined number of perforations per line, the number ofperforations per line being substantially in excess of the number oflines of perforations, each of said pair of ribbons having axially outerends sandwiching therebetween the axially inner ends of said pair ofknife blade contacts, and each of said pair of ribbons having a pair offlexible bends situated adjacent to one of the axially outer endsthereof;

(2) a filled of quartz sand inside of said casing embedding said pair ofribbons; and

(1) two pairs of insulating plates each substantially coextensive withsaid lattice pattern area of one of said pair of ribbons and eachaffixed to one of said pair of ribbons on juxtaposed sides thereof.

2. An electric high interrupting capacity fuse compris ing incombination (a) a substantially tubular casing of insulating materialhaving a predetermined inner diameter;

(12) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined widthbut slightly less than said diameter each projecting from the outside ofsaid casing through the end surface of one of said pair of terminal capsinto the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a. metal having arelatively high conductivity and a relatively high fusing pointapproximately equal in width to said predetermined width conductivelyinterconnecting the axially inner ends of said pair of blade contacts,each of said pair of ribbons including a lattice pattern area of necksconnected in parallel and of serially connected necks, said latticepattern area being formed by substantially transverse lines ofperforations each including a predetermined number of perforations perline, the number of perforations per line being approximately twice thenumber of lines of perforations, each of said pair of ribbons havingaxially outer ends sandwiching therebetween the axially inner ends ofsaid pair of knife blade contacts, each of said pair of ribbons having apair of flexible bends situated adjacent to one of the axially outerends thereof;

(e) a filler of quartz sand inside of said casing embedding said pair ofribbons; and

(f) two pairs of insulating plates each substantially coextensive withsaid lattice pattern area of one of said pair of ribbons and eachaffixed to one of said pair of ribbons.

3. An electric high interrupting capacity fuse comprising incombination:

(a) a substantially tubular casing of insulating material having apredetermined inner diameter;

(/5) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined widthbut slightly less than said diameter each projecting from the outside ofsaid casing through the end surface of one of said pair of terminal capsinto the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having arelatively high conductivity and a relatively high fusing pointapproximately equal in width to said predetermined width conductivelyinterconnecting the axially inner ends of said pair of blade contacts,each of said pair of ribbons including a lattice pattern area of necksconnected in parallel and serially connected necks, said lattice patternarea being formed by substantially transverse lines of perforations eachincluding a predetermined number of perforations per line, the number ofsaid transverse lines being three and the number of perforations perline being at least six, each of said pair of ribbons having axiallyouter ends sandwiching therebetween the axially inner ends of said pairof knife blade contacts, each of said pair of ribbons having a pair offlexible bends situated adjacent to the axially outer ends thereof;

(6) a filler of quartz sand inside of said casing embedding said pair ofribbons; and

(f) two pairs of insulating plates each substantially coextensive withsaid lattice pattern area of one of said pair of ribbons and eachaflixed to one of said pair of ribbons.

4. In combination an electric circuit having a predetermined circuitvoltage and an electric high interrupting capacity fuse inserted intosaid circuit, said fuse including:

(a) a substantially tubular casing of insulating material having apredetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined widthbut slightly less than said diam eter each projecting from the outsideof said casing through the end surface of one of said pair of terminalcaps into the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having arelatively high conductivity and a relatively high fusing pointapproximately equal in width to said predetermined Width conductivelyinterconnecting the axially inner ends of said pair of blade contacts,each of said pair of ribbons including a lattice pattern area of necksconnected in parallel and serially connected necks, said lattice patternarea being formed by substantially transverse lines of perforations eachincluding a predetermined number of perforations per line, the number ofsaid transverse lines being equal to said circuit voltage divided by 200and the number of perforations per line being approximately twice saidnumber of lines, each of said pair of ribbons having axially outer endssandwiching therebetWeen the axially inner ends of said pair of knifeblade contacts, each of said pair of ribbons having a pair of flexiblebends situated adjacent the axially outer ends thereof;

(2) a filler of quartz sand inside of said casing embedding said pair ofribbons; and

( two pairs of insulating plates each substantially coextensive withsaid lattice pattern area of one of said pair of ribbons and eachaffixed to one of said pair of ribbons.

5. In combination an electric circuit having a circuit voltage of 600volts and an electric high interrupting capacity fuse inserted into saidcircuit, said fuse includmg:

(a) a substantially tubular casing of insulating material having apredetermined inner diameter;

(b) a pair of terminal caps closing the ends of said casing;

(c) a pair of aligned knife blade contacts having a predetermined widthbut slightly less than said diameter each projecting from the outside ofsaid casing through the end surface of one of said pair of terminal capsinto the inside of said casing;

(d) a pair of spaced thin sheet metal ribbons of a metal having arelatively high conductivity and a relatively high fusing pointapproximately equal in width to said predetermined width conductivelyinterconnecting the axially inner ends of said pair of blade contacts,each of said pair of ribbons including a lattice pattern area of necksconnected in parallel and serially connected necks, said lattice patternarea being formed by but three transverse lines of perforations eachincluding about six perforations per line, each of said pair of ribbonshaving axially outer ends sandwiching therebetween the axially innerends of said pair of knife blade contacts, each of said pair of ribbonshaving a pair of flexible bends situated adjacent the axially outer endsthereof;

(e) a filler of quartz sand inside of said casing embedding said pair ofribbons; and

(1) two pairs of insulating plates each substantially coextensive withsaid lattice pattern area of one of said pair of ribbons and eachaffixed to one of said pair of ribbons.

References Cited in the file of this patent UNITED STATES PATENTS1,278,322 Eustice et al. Sept. 10, 1918 1,290,860 Bender Jan. 7, 19192,313,373 Sundt Mar. 9, 1943 2,665,348 Kozacka Jan. 5, 1954 2,864,917Sundt Dec. 16, 1958 2,988,620 Kozacka June 13, 1961 FOREIGN PATENTS20,483 Great Britain Sept. 19, 1902 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 5,152,253 October 6, 1964 FrederickJ, Kozack'a It is hereby certified that error appears in'theabovenumbered patent reqiiring correction and that the said Letters Patentshould read as oorrectedbelow.

Column 1, line 59, for "neck" read necks column 3, line 68, for "a" readthe column 6, line 17, 'for "X 8.1'ld X4" read x and x column, .7 line53, column .8 lines l3 and 48 column 9 line- 11, and column 10 line 13after "bends", each occurrence, insert each column 7, line 55, for"filled" read filler column 7 line 57', column 8.,- lines 17 and 52,column 9, line 15, and column 10, line l7, strike out "pairs of" eachoccurrence I Signed and sealed this 24th 'day of August 1965 (SEAL)Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Atlnsting Officer Commissioner ofPatents,

UNITED STATES PATENT OFFICE Q CERTIFICATE OF CORRECTION Patent No 3,152,235 October 6, 1964 Frederick J, Kozecka It is hereby certified thaterror appears in'the above numbered patent reqliring correction and thatthe said Letters Patent should read as oorrectedbelow.

Column 1, line 59, for "neck" read necks column 3,

line 68, for "a" read the column .6, line 17, for "x mand X4" read X3and 20 column, [7 line 53, column .8 lines 15 and 48, column 9, line 11,and column 10, line 13, after "bends", each occurrence, insert eachcolumn 7, line 55, for "filled" read filler column 7, line 57', column8,- lines 17 and 52, column 9, line 15, and column 10, 'line 17, strikeout pa irs' of" each occurrence. s

Signed and sealed this Z4th-"day of August 1965.,

(SEAL) Attest:

ERNEST w. SWIDER EDWARD J. BRENNER Ancsting Officer Commissioner ofPatents

1. AN ELECTRIC HIGH INTERRUPTING CAPACITY FUSE COMPRISING INCOMBINATION: (A) A SUBSTANTIALLY TUBULAR CASING OF INSULATING MATERIALHAVING A PREDETERMINED INNER DIAMETER; (B) A PAIR OF TERMINAL CAPSCLOSING THE ENDS OF SAID CASING; (C) A PAIR OF ALIGNED KNIFE BLADECONTACTS HAVING A PREDETERMINED WIDTH BUT SLIGHTLY LESS THAN SAIDDIAMETER EACH PROJECTING FROM THE OUTSIDE OF SAID CASING THROUGH THE ENDSURFACE OF ONE OF SAID PAIR OF TERMINAL CAPS INTO THE INSIDE OF SAIDCASING; (D) A PAIR OF SPACED THIN SHEET METAL RIBBONS OF A METAL HAVINGA RELATIVELY HIGH CONDUCTIVITY AND A RELATIVELY HIGH FUSING POINTAPPROXIMATELY EQUAL IN WIDTH TO SAID PREDETERMINED WIDTH CONDUCTIVELYINTERCONNECTING THE AXIALLY INNER ENDS OF SAID PAIR OF BLADE CONTACTS,EACH OF SAID PAIR OF RIBBONS INCLUDING A LATTICE PATTERN AREA OF NECKSCONNECTED IN PARALLEL AND OF SERIALLY CONNECTED NECKS, SAID LATTICEPATTERN AREA BEING FORMED BY SUBSTANTIALLY TRANSVERSE LINES OFPERFORATIONS, EACH OF SAID LINES OF PERFORATIONS INCLUDING APREDETERMINED NUMBER OF PERFORATIONS PER LINE, THE NUMBER OFPERFORATIONS PER LINE BEING SUBSTANTIALLY IN EXCESS OF THE NUMBER OFLINES OF PERFORATIONS, EACH OF SAID PAIR OF RIBBONS HAVING AXIALLY OUTERENDS SANDWICHING THEREBETWEEN THE AXIALLY INNER ENDS OF SAID PAIR OFKNIFE BLADE CONTACTS, AND EACH OF SAID PAIR OF RIBBONS HAVING A PAIR OFFLEXIBLE BENDS SITUATED ADJACENT TO ONE OF THE AXIALLY OUTER ENDSTHEREOF; (E) A FILLED OF QUARTZ SAND INSIDE OF SAID CASING EMBEDDINGSAID PAIR OF RIBBONS; AND (F) TWO PAIRS OF INSULATING PLATES EACHSUBSTANTIALLY COEXTENSIVE WITH SAID LATTICE PATTERN AREA OF ONE OF SAIDPAIR OF RIBBONS AND EACH AFFIXED TO ONE OF SAID PAIR OF RIBBONS ONJUXTAPOSED SIDES THEREOF.